SiC-based materials are employed for a large number of different uses, in particular where high stability at high temperatures or high levels of resistance to corrosion are required. Highly porous and thus also lightweight, SiC-based ceramics are increasingly required as catalyst carriers, combustion aids, Insulating materials, substrate materials or for gas heating in pore burners or for solar installations and for exhaust gas cleaning at high temperatures as filter materials.
SiC-materials on an SiC-base are produced either on the basis of SiC-powders (U.S. Pat. No. 6,582,796) or from a mixture of carbon-bearing or silicon-bearing materials. By way of example a carbon-bearing compound is shaped to provide a molded body, then pyrolyzed and converted into an SiC body by melt infiltration with liquid silicon (US No. 2003/0180538). Alternatively a carbon-bearing powder and a silicon-bearing powder can also be shaped to provide a molded body and then converted to SiC (U.S. Pat. No. 4,481,179).
Upon extrusion however the extrusion nozzles are subjected to a high level of wear. In addition the production of stable molded bodies which have a passage structure, in particular a high passage density and a small wall thickness, is not possible in adequate quality. Structures of that kind however are required in particular in the catalyst art and in filter technology. Silicon carbide has a very poor adhesion capability for catalysts. Consequently it is desirable not only to improve the stability of the molded body but in particular also the adhesion properties thereof, in particular for catalysts and catalyst materials.
The object of the invention is to provide an improved process for the production of porous SiC-based ceramics, in which the molded body can be more easily extruded, wear and abrasion at the molding tools is reduced and/or the energy consumption is low.
A further object is to provide a process for the production of porous SiC-based ceramics which permits the extrusion of very fine passage structures with a high passage density and a small passage wall thickness.
A further object is to provide a porous ceramic SiC-based molded body with a definable pore structure and adequate porosity and fine-cell nature (passage density), which is preferably suitable as a catalyst carrier and/or filter and/or which further preferably has excellent temperature resistance and chemical and mechanical resistance.
A further object is to provide a mechanically stable porous ceramic SiC-based molded body which has very fine passage structures with a high passage density and which can preferably be produced by extrusion.
A further object is to provide a porous ceramic SiC-based molded body whose article has improved adhesion properties, in particular for catalysts or catalyst materials.